1. Field of the Invention
The present invention relates to a seam construction for an industrial fabric, in general, and, in particular, to a seam construction for a single layer industrial fabric having an uneven shed pattern. Most particularly, it relates to a papermaker's forming fabric in the described construction.
2. Prior Art
The prior art has recognized for some time the advantages to be achieved in seaming a woven fabric to form an endless belt for use in industrial process such as papermaking. In the dryer and press sections of the papermaking machines, it has long been accepted practice to seam the fabric. More recently, the papermaking art has been attempting to produce acceptable seams in forming fabrics.
Various seam constructions will be known to those skilled in the art. One type of known seam is the clipper hook seam. In this type of seam, the clipper hooks, generally of stiff wire, are crimped to each end of the fabric and the eyes on the ends of the fabric are meshed together and a cable inserted to complete the seam. Another known seam is the multifilament seam. In this seam, multifilament yarn connecting loops are woven into a webbing that has been sewed to the fabric body. Another known seam is the pin seam. In this construction, connecting loops of machine direction monofilament yarns are woven back into the fabric body. Generally, the back woven yarns are woven to complement the weave pattern of the fabric body. The loops are intermeshed and joined as a seam by a monofilament connecting pin or pintle. Another known seam is the spiral seam. This seam is generally formed of all plastic materials. Loops of a continuous spiral are affixed to either end of the fabric; the loops are intermeshed and interconnected with a pintle wire to form the seam.
Regardless of the seam construction utilized, it has been recognized by the art that the seam characteristics are critical to the performance of a papermaker's fabric. Likewise, it has been recognized that the seam must resemble the body of the fabric as closely as possible. In addition, the seam must be uniform and generally share the sheet forming characteristics of the body of the fabric. Although certain applications may be more tolerant of seam constructions, which may cause marks on the product, it is almost always desirable to minimize the differences between the seam and the fabric body.
In papermaking, seam construction has long been recognized as critical. As higher speeds are attained in the papermaking machine, the seam has become increasingly critical. In addition to increased speed, the desire for reduced fabric caliper has lead to additional pressures for a generally uniform seam within a reduced fabric plane. In addition to the need for uniform seams in higher speed and lower caliper fabrics, seam durability is critical to the operation of and the durability of the fabric in production.
Although a number of the above seams have been successful, there are some remaining limitations in the prior art seam constructions. Generally, as the fabric thickness or caliper is reduced, the thickness of the seam must be reduced. This becomes especially critical in single layer fabrics. The desire for reduced seam caliper has lead to an associated reduction in the caliper of the seaming elements. However, in single layer fabrics, - the pintle element has been reduced to the lower limits of acceptability. This has resulted in premature seam failure which renders an otherwise useful fabric unproductive. The problems in single layer fabrics have been especially difficult in single layer fabrics with uneven sheds., i.e. three, five, seven, etc. shed fabrics. Earlier attempts to seam such fabrics in papermaking applications have resulted in a defect known as a pin hole.
In view of the above, it is the general object of the present invention to provide an improved seam construction that is especially useful for lower caliper, single layer industrial fabrics having uneven shed patterns. In particular, it is an object of this invention to provide a coil seam construction for single layer fabrics, woven in odd shed repeats, for use in paper forming applications where minimal seam marking is acceptable.